This invention relates to an apparatus and method for mixing a gas and a liquid. In one aspect, this invention relates to an apparatus and method for mixing a carrier gas with an atomized liquid while in another aspect, this invention relates to the formation of a mixture of carrier gas and vaporized liquid with little, if any, entrained droplets. In yet another aspect, the invention relates to an apparatus and method for applying a preservative to a perishable product.
The preservation of perishable products has been and continues to be the focus of considerable commercial interest. By extending the shelf life of a food product, e.g., a baked good, considerable economic value can be added to that product. Approaches to this end are many and varied, e.g., tight control of storage conditions, packaging, post and in situ applications of preservatives, and various combinations of these and other techniques are known and in practice to one extent or another.
In the context of baked goods, e.g., muffins, crumpets, scones, bagels, cookies, breads, etc., all of these techniques are in use, e.g., frozen or refrigerated storage, anaerobic packaging, and the addition of preservatives either to the batter or mix from which the baked good is prepared, or the application of a preservative to the finished baked good. With respect to the latter, the application of a small amount of acetic acid to a finished baked good, e.g., a crumpet, can extend the shelf life of the baked good from a typical 6–8 days to an extended 14–16 days (all other conditions, e.g., packaging, storage conditions, etc., being equal). One problem, however, in the application of a preservative to a food product is to apply the preservative in a manner that does not interfere with the natural sensient properties of the product, e.g., taste, smell, texture, etc. In the case of applying acetic acid to a finished baked product, too much acetic acid can impart an unwanted tartness to the product.
Another problem with the application of a preservative to the finished baked good is consistent application of the preservative in a production line setting. Commercially distributed baked goods, along with most other commercially manufactured and distributed perishable goods, are made in large quantities, and consistency from one item to the other is important to the commercial success of the product line. In the case of applying acetic acid to baked goods, the amount of acetic acid applied to the first baked good in the production cycle should be essentially the same as the amount of acetic acid applied to the last item in the production cycle (and all items throughout that production cycle, for that matter). This can be difficult to control over extended periods of time due to, among other things, variations in the temperature of the equipment, the preparation and delivery of the acetic acid to the finished product, and the like.
For example, the application of acetic acid as a preservative to a finished baked good typically begins with the conversion of liquid acetic acid to gaseous acetic acid. This conversion is accomplished by any one of a number of different procedures, e.g., flash evaporation, atomization, etc., and the gaseous acetic acid is then transported, typically by a carrier gas, e.g., carbon dioxide, to a treatment chamber. Finished baked goods are fed on a batch basis to the chamber in which they are exposed under predetermined conditions to the acetic acid, removed from the chamber, and then the cycle repeats. One common problem with this technique is that the gaseous acetic acid often has entrained within it small droplets of liquid acetic acid and these droplets, when deposited on the finished baked good, can constitute an overdose of preservative and impart a tartness to the product. The droplets originate from either incomplete vaporization of the acetic acid and/or as a condensate from the gaseous acetic acid as it is transported from a vaporization zone to the treatment chamber. Similar problems exist, of course, with the application of other gaseous preservatives to other perishable products.